Only You Understand
by theunknownvoice
Summary: Rukia has learned to live with guilt but when an investigation about Aizen's experiments with hollows unearths information about Kaien, will she be able to cope? Or will she fall right into a trap?
1. Hidden in the Files

Only You Understand

By: theunknownvoice

Disclaimer: I don't own Bleach.

A/N: I promised another KaiRuki and I delivered. So read and review pretty please.

Chapter 1: Hidden in the Files

Aizen's legacy of experimentation ran throughout Soul Society. Many of the files were encrypted and hidden but that didn't stop Matsumoto and Hitsugaya for searching for them. Too many secrets had been hid from the other shinigami.

Matsumoto hated paperwork but right now she would relish it. At least in the office she could fall asleep while her cute little taicho filled out paperwork. The office couch was comfortable enough for her to lie down on.

The Central 46's archives were full of classified research.

"What are we doing here Taicho?"

Hitsugaya shook himself out of the research. It was dry reading even for him and he was grateful for Matsumoto's interruption.

"We're finding the files that Aizen used for his research."

"Taicho, do you really believe he has found a way to combine a hollow and a shinigami?"

Hitsugaya could see the worry in her blue eyes. His fukutaicho had been through hell because of Aizen. Gin's betrayal was enough to push Matsumoto over the edge. She had spent her days in a sake caused stupor. She mourned with Hisagi and Izuru the betrayal of the captains and the sake bottle was never empty.

Hitsugaya had taken the sake bottles and thrown them out. He had given Matsumoto work in order to prevent her from drinking. Members of the other divisions especially the third and ninth fukutachios, Matsumoto's drinking buddies, were not allowed in the office.

She wanted to die, and Hitsugaya wouldn't let her kill herself.

Gin had hurt her just as Hinamori had hurt him and he wasn't going to allow his fukutachio to suffer alone. That was why when the sotaicho asked him to lead in an investigation of Aizen's research, Hitsugaya had said that he would do it as long as Matsumoto was his assistant.

For the first time Hitsugaya could admit he was afraid not for himself but for Matsumoto. He couldn't lie to her. He couldn't pretend there was nothing wrong.

"I'm sure he has."

Matsumoto shuddered as she turned back to the files.

-

Mayuri Kurotsuchi hated that man.

He had always hated him and he always would hate him. That bastard Urahara had everything Kurotsuchi wanted.

He was famous for his developments and Kurotsuchi had one great success. Nemu was his creation and she was loyal to him. The most faithful and devoted of the dogs that served him and that was why he would never suspect her of going through his files or doing what she was doing now.

"Hello Nemu-chan."

Nemu tried not to smile at the man who had been a second father to her. The communication device had been one of Urahara's inventions and it seemed appropriate that he had a way to be contacted.

"It is good to Urahara-san."

"I take it old robot face doesn't know you're contacting me?"

"Mayuri-sama isn't here at the moment. Sotaicho Yamamoto asked that you be contacted by our division and I decided to be the one to follow the order.

Urahara bit back a smile. "I'm glad it's you, Nemu, and not your father. So what can I do for Soul Society?"

"Yamamoto-sotachio wants to know what you know about Aizen's hollow development."

"I can tell you my suspicious and some of what I know but it isn't much."

"Please Urahara-san…we need to know."

Kisuke Urahara knew then that he could trust Nemu. The girl wouldn't judge and she wasn't like her father. Her loyalty lay strictly with Soul Society.

"Be prepared to take notes."

"Hai, Urahara-san," Nemu said as she pulled at a notebook.

Urahara chuckled the kid was good.

-

Yamato sat in his chambers. Fukutachio Kurotsuchi had brought him her notes regarding the hollow experiments. The girl had been quick about it and Yamamoto suspected she didn't want her father to know she had contacted Urahara.

He could understand the young woman's worries and had already decided that if she was this loyal then perhaps she should be allowed to work on more projects without her father's constant supervision.

It was worth considering.

The knock on the door shook the old man from his thoughts. He wasn't expecting his fukutaicho Sasakibe to arrive for some time.

"Enter."

He glanced at the two shinigami before him. "I had assumed Hitsugaya-taicho that it would take you and Matsumoto-fukutachio several weeks to have finished your research."

"Sir, you informed my taicho that if we found anything of interest to bring to you right away," Matsumoto said.

"Yes, I did."

Hitsugaya moved forward with a file in his hands. "I believe sotaicho that you would want to have a look at this."

"_Come on Taicho. Can't we take a break?"_

"_Matsumoto we'll break in another hour. We still haven't scratched the surface."_

_Hitsugaya continued to focus on the file in front of him. Most of it appeared to be about research involving gigais but one never knew if there was something hidden more in the text._

"_Taicho?"_

_He glanced at his fukutaichou._

"_Can we take a break now?"_

"_It's no like I said five seconds ago."_

_This was really boring. Apparently gigais had some weaknesses but most shinigami knew that but this was an in depth study of how to perfect a gigai. Each step of the research had been described._

"_Taicho?"_

"_No."_

"_But Taicho—"_

"_MATSUMOTO!"_

_She giggled. "I knew you'd react that way Taicho."_

_Hitsugaya simply rolled his eyes. That woman could drive him crazy._

_The rest of the hour passed in silence. So far he had read about the gigais and a few experiments with mod souls. There was nothing too special._

_He was about to call it lunch when he glanced at Matsumoto._

_Her face was ashen as she looked at the file in front of her. She quickly glanced away from the file and ran to the trash can to throw up. Hitsugaya grimaced at the sound of her retching and reached for the file himself. The minute he read the title he too felt sick._

Yamamoto read the file after hearing the lengthy explanation.

"I want you to keep this information between yourselves. However, I will allow Kuchiki Rukia to be told."

Matsumoto swallows. She remembers the lonely look on Rukia's face the day after she had come back from fighting the hollow. Matsumoto had lost a comrade that day but Rukia had lost someone even more precious.

Rukia had been consumed by guilt and here was the chance to fix that and then Yamamoto's words bring the world crashing down.

"Of course Kuchiki Byakuya must be consulted first."

Matsumoto knows then that Rukia won't be told the truth. The truth that the hollow that merged with Shiba Kaien wasn't dead. That somewhere a piece of Shiba Kaien still exists but if Kaien was one thing it was a survivor.

-

"_You always were an arrogant prick."_

_The sixth division captain tried to reign in his temper. He didn't need this from the thirteenth bantai's fukutaicho especially in his own home._

"_I don't deserve this from you. This isn't any of your business. Rukia is under my care and she is my sister."_

"_Sister or replacement for your dead wife?" Kaien's eyes flashed dangerously._

"_Don't you dare insinuate such a thing."_

"_You want to handicap Rukia and prevent her from earning rank. You want to keep her sheltered just like Hisana."_

"_This isn't your business."_

"_She's my subordinate."_

"_Since when do you ever go this far for a subordinate?"_

_Kaien's hands were on his zanpakuto but he didn't draw. "If anything happens to her because of you I swear you'll regret it."_

"_This that a threat Shiba-san."_

"_It's a promise Kuchiki-san."_

Byakuya blinked back the memory. He had been friends with the other children in the noble families since childhood. It had been friendships forged by their parents' desires that they become close.

It wasn't that Byakuya Kuchiki hadn't respected Kaien Shiba but they had been so different. Kaien was known to be the type of person to care about his subordinates but something was different about this. Byakuya could tell and so he watched.

_The training room for the thirteenth bantai was normally empty. Byakuya didn't think much of it until he heard a familiar voice._

"_You need to hold a zanpakuto like this. That stance will get you knocked about by a really strong hollow."_

"_But Kaien-dono—"_

"_There's no buts Kuchiki. You want to live right?"_

"_Hai."_

"_Then learn to hold your zanpakuto properly."_

_Byakuya can see her swing the wooden sword as she prepares to attack her vice-captain. She's getting faster and more confidence. The two practice sword and the sound of wood on wood echoes._

"_Good Kuchiki, you'll be better than me in another few centuries. Or at least better than I am now."_

_Rukia only rolls her eyes. "I'll beat you one day, Kaien-dono."_

_Kaien grins. "I seriously doubt it."_

At first Byakuya had reasoned it as some type of fondness for a subordinate. Kaien had recognized that Rukia was lonely and had decided to help her. It was nothing more than that. That was until the day we saw them at the lake.

"_As long as you're in my division I'll stand by you. Even if I die."_

The realization had hit Byakuya like a lightening bolt: He's in love with her.

Byakuya knew Kaien well enough to know that the man never made promises he didn't intend to keep. All of his actions towards Rukia had shown true affection but it wasn't the big brother in Kaien coming out. Kaien was protective of Rukia but it was more than that.

"_Sister or replacement for your dead wife?"_

Why hadn't he heard the jealous in his friend's voice then?

No, he could not tell Rukia of this. This would destroy her and break her. Byakuya only now had the chance to be the type of brother he wanted to be.

Byakuya glanced at the paperwork in front of him and looked towards the two members of the tenth bantai.

"Rukia is to not be informed."

Matsumoto only bit her lip.

To be continued….


	2. I Never Promised

Chapter 2: I Never Promised

Disclaimer: Bleach does not belong to me and never will.

Rangiku Matsumoto was never big on doing paperwork or even reading paperwork. She preferred to spend hours talking to people instead of reading through reports. Reports were dull but it was better than seizing about Byakuya Kuchiki being a complete and total ass.

"_You can't do that Kuchiki-taicho! You can't! Rukia-chan needs to know. She has suffered enough because of this! This isn't fair!"_

_Byakuya's face went white and his glare was directed at her. He was about to bite out some _

"_Matsumoto, you have no right to talk to Kuchiki-taicho like that. Kuchiki-taicho, I apologize for my fukutachio. She has not the right to speak to you in such a manner."_

"_I would remind you both," Byakuya said coolly, "that it is my decision whether Rukia be informed. I do not need your approval Matsumoto-san nor do I seek it. Now I request that you both leave my office."_

_The two leaders of the tenth bantai bowed slightly and then left._

_Hitsugaya turned towards his subordinate his green eyes barely containing their fury. "You are not to question what decision is being made. The sotaichio said it was in Kuchiki-taicho's hands whether or not Rukia-san would be informed."_

"_But Taicho, it's wrong. Rukia-chan suffered a lot. Shouldn't she be allowed to know the truth?"_

"_Again Matsumoto it is not our decision. It is Kuckiki-taichio's."_

"_He is a heartless teme. Like he cared about Rukia-chan before this. He couldn't—"_

_Hitsugaya turned towards her his eyes colder than usual. "That is enough! You must control how you feel. I don't like it either but it is not our decision."_

_He marched off towards the record's room leaving her standing alone._

She was still angry at her taicho but he did have a point. She couldn't do anything about this instead she would focus on learning more about what had happened to Kaien.

The files were confusing and she stared at them in complete despair. She couldn't understand half of this scientific jargon.

"Do you need some help Rangiku-san?"

Matsumoto looked up and thanked kami that this was the person Yamamoto had sent to them to explain the science. The rest of the twelfth bantai freaked her out.

-

Nemu didn't know what to expect. She had never been summoned here before so it placed her in a precarious position. Rarely did she ever leave the twelfth bantai's area. There was always so new experiment to work on or someone her father wanted her to specifically keep an eye on.

She did go to the Women's Shinigami meetings but that was because it was required. Despite her father's best efforts to isolate her she had found some companionship. But most people overlooked her. So it was a rare surprise that she had personally been requested by the Sotaicho to come to the first bantai.

"Kurotsuchi-fukutachio, come in."

She nodded at the elderly man. His appearance was a bit deceptive. No one would've guessed he was the most powerful captain in the Gotei 13.

He was leaning on the wooden walking stick that concealed his zanpakuto.

"You summoned me sotaichio."

"Sit down. I wish to speak to you about a project I have in mind."

Nemu obeyed automatically. She didn't know what to expect from this man but the fact he had a project for her intrigued her.

"I wish for you Kurotsuchi-fukutachio to read through Urahara Kisuke's research. You will be assisted Hitsugaya-taicho and Matsumoto-fukutaicho in their investigation. The scientific facts of the files they are reading a slightly confusing to them and they need further explanation. I, myself, rarely understand all that such documents contain considering it was not my field of study."

She bowed her head lower. "I am honored sotaicho but may I ask why you do not approach Mayuri-sama? Surely he could explain the contents of the files better than I could."

"He is too busy with his bantai and I prefer it be you."

Nemu nodded she already understood the underlined meaning. The sotaicho trusted her. Her father would be tempted to try the experiments. Nemu already knew of his goal to surpass Urahara. It was why she had been created.

"I accept."

-

Hitsugaya Toshiro glanced at the file in front of him. He had to make a decision. It wasn't like he agreed Byakuya's decision. In fact he was very much against it but there was also the fact that it wasn't in his hands.

Matsumoto had been angry and Hitsugaya hated the fact that he couldn't just agree with her. She was right but he needed to support the rules. Sometimes it sucked being a straight arrow.

"_Rangiku?"_

_Matsumoto turned to look at him. It was so rare for him to call her by her first name and he only did it when he was very serious._

"_Toshiro?"_

"_Rangiku, why do you care so much about Rukia being told about Shiba-fukutaicho?"_

_Matsumoto stiffened slightly before replying. "Rukia-chan was hurt so much. She thinks she killed Shiba-san. They were close taicho. They were always together. They were friends. If one of my friends died and I thought I was responsible I'd want to know the truth."_

_There were tears in her eyes. It was small tears but they were there._

"_Rangiku, are you alright?"_

"_He was my friend too. He was one of the few fukutaicho's that it was easy to talk to. And he never judged my drinking."_

_Hitsugaya nodded he knew that some of the other soul reapers talked about Matsumoto as a drunk._

"_It's just not fair taicho. No one should have to live with that kind of guilt. Rukia-chan—she loved him taicho. She really loved him and she was never the same after his death."_

Hitsugaya had never met Shiba Kaien. He didn't know much about the man except that he inspired loyalty in those that knew him. Matsumoto had lost many friends but perhaps it was the fact that Rukia was her friend too.

Maybe he had wanted to understand. That was the only reason that he would go visit Ukitake. Not that he didn't like the older captain it was just that Hitsugaya wasn't too fond of sweets.

"_Toshiro-kun, I didn't expect to see you today."_

_Hitsugaya smiled at the older man. Ukitake was confined to his bed again. Unohana-taicho had said that the thirteenth squad captain had pushed himself to hard lately._

"_I figured I might as well check on you."_

"_I heard about the investigation. How is it coming?"_

_Hitsugaya internally winced. He couldn't inform Ukitake of his findings even though he wanted to. The sotaicho had made him swear to keep his silence._

"_It is going well. I was wondering something today though."_

"_Oh? What could possibly make you curious Toshiro-kun?"_

"_I wondering, why you haven't assigned yourself a new fukutaicho. Surely it isn't easy for you."_

_Ukitake merely waved his hand smiling though his eyes were hardening. "Sentaro and Kiyone both do the job of a fukutaicho."_

"_You don't want to replace Shiba-san."_

_Ukitake visibly flinched at Toshiro's candor. "I'll admit replacing him isn't something I desire."_

"_He was a good fukutaicho?"_

_Ukitake raised an eyebrow. It appeared that Hitsugaya was curious about Kaien. Why he didn't know but it he would bet it had something to do with Aizen's experiment involving Kaien._

"_He was arrogant, a hard worker, loud and very social. He had a way about making people open up. Like Rukia-chan. She came to us so quiet and afraid. A few months earlier she had been Rukongai and then she was a noble. It was a shock to her."_

"_Wasn't he married?"_

"_Miyako, she was kind but it was an arranged marriage. They were friends but I don't know how Kaien really felt about her. They always seemed to have a distance between them. When she died I think he felt responsible."_

_Hitsugaya took it in._

"_He was close to Rukia?"_

"_Rukia was his favorite squad member. He trained himself."_

_Hitsugaya was mildly surprised. The fact that fukutaicho had taken it on himself to train her was very significant._

"_Toshiro, why are you asking this?"_

_He glanced at Ukitake. "Let's just say I was curious."_

Hitsugaya looked again at the report. So many lives had been destroyed by this one experiment. What right did Aizen have to do this?

But Aizen didn't care about lives. He had even gloated the fact that he had done this to torture Rukia. Rukia already blamed herself for this.

She had been close to her fukutaicho much like Hitsugaya's closeness to Matsumoto. If something like this had happened to Matsumoto wouldn't he want to know? Wouldn't he deserve to know?

Hitsugaya made up his mind. He headed out of his office with the file in his hand.

-

Byakuya had been surprised at the out burst of Matsumoto Rangiku. She should have controlled herself. Hitsugaya hadn't jumped her soon enough in his opinion. He had his reasons. They weren't there that night. They hadn't seen Rukia like he had.

_His sister was crying. He could hear throughout the entire manor. Blood dripped on the floor. She was soaked in._

"_Rukia, what happened to you?"_

_He was scared. The great Byakuya Kuchiki was scared._

"_Rukia, what is wrong?"_

_She sobbed harder. "Kaien-dono, he's dead. I stabbed him. I had no choice. The hollow it—"_

_He marched to the thirteenth division office where Ukitake explained everything._

_He let Rukia mourn. He understood. It had hurt when he lost Hisana and Rukia had been close to Kaien. But the grief bothered him._

_Three weeks later he requested his sister. She had been so quiet and her eyes were red rimmed. She bowed her head and knelt down in front of him._

"_Rukia, you can not remain upset about this. You must move on. People die and we must accept that."_

"_Hai ni-sama."_

_He never thought it would hurt to hear those words._

_He didn't want to admit that his sister loved that prideful idiot._

He couldn't do that her again. He had tried to ignore the fact that she loved Kaien. He knew his sister worshipped the ground Kaien walked on. She couldn't know this. She couldn't it would destroy her.

-

_The rain was pouring hard. It was dark. She wasn't used to the darkness._

_Fighting hollows at night was always dangerous but there was something in the air that night. This hollow had destroyed a large group._

_Her blood ran cold as they moved further and further following the trail. There were bodies left behind and the blood soaked the ground in thick pools. She moved faster to keep up with the two considerably taller men._

_She had never seen the captain out fighting like this. Normally he was too sick and confined to a hospital bed. Now he was moving quickly keeping up with his fukutaicho. _

_She could barely look at her fukutaicho without crying. His blue eyes that normally were laughing were glazed with pain. She could see the guilt in the way he moved. He was too quiet. She was used to him shouting and bragging._

_She moved quickly following them. The hollow was the strangest looking one she had ever seen. The head was large and the body wasn't normal. There was no standard looking hollow._

"_I'll go in to scout its capability." Her hand was on her zanpakuto and she was ready._

"_Permission to go in alone, sir."_

_Ukitake merely nodded._

"_Kaien, no."_

"_Rukia, he is fighting for his pride and his wife's pride. Would you rob him of that?"_

_She should never have let him go alone. It was wrong. Only something bad would happen because of this._

_It becomes hazy after the hollow possesses him. And she's scared._

_Run. Run. Run._

_Don't look back._

_He's hurting. I don't want him to hurt._

_I love him._

_I don't want him to hurt._

_No, turn around._

_I can't leave him there. I won't leave him there. I'll do whatever it takes to make him stop hurting._

_She barely feels her hands move as she turns to face him and he is impaled. And then she sees the red tainting her skin._

_His weight was against her shoulder. He was heavy and she could feel his blood soaking down her shirt tainting her. All she could do was hold him._

"_I'm sorry. I'm sorry. Thank you. My heart can stay here."_

"_You don't have to thank me. I couldn't stand seeing you in pain._

_His breathing was growing more ragged as she clung to him burying herself in him._

"_Thank you."_

_He kept murmuring and she felt his body stiffen._

"_No! Kaien! Kaien! Don't die Kaien! Don't die!"_

_Her scream echoed through the woods but there was no reply. His eyes were open and his weight was against her but his soul wasn't there._

_She had killed him._

Rukia shook out of the dream. Her body jerking considerably as she spasmed. The memory even after all these years was still fresh and vivid. She could still feel his blood staining her skin.

She buried her face further into her pillow and sobbed. It hurt too much.

A few hours later she was acceptable. She breakfast with her brother and moved through the day's events automatically. She still worried about Ichigo who was back in the human world.

As soon as she could she would go see him. He was in some ways a painful reminder to her. His appearance hit her too hard. Even they fact he was loud and argumentative was painful. But Ichigo made some of her ache go away just by existing.

He had saved her life. She had saved his. They were even now but she knew they never would not owe each other. Debts like theirs couldn't be wiped clean.

The division office was busy. She could hear the two third seats arguing about who was more loyal to Ukitake. At least this morning they had posted the mail on time.

Rukia barely glanced at her inbox. She wasn't big on checking on her mail but at least she could do that today.

A lot of it was just notices about her report. There were a few orders but no long term assignments. Then she felt the thickness of an envelope.

**To Rukia Kuchiki, classified information.**

She gazes at critically before taking it back to room. Alone in the gigantic manor she opens the envelope. Her hands finger the paperwork and then she sees the report: **Transmutation of Shinigami and Hollow.**

As she reads over it her nightmare begins again and she passes out.

To be continued….

A/N: I know it's dramatic for Rukia to pass out but she just found out what exactly happened to Kaien so I think she's allowed to. Sorry if it seems OC but if I found that someone I thought I'd killed was alive then I would probably have the same reaction.


End file.
